This study is designed to provide badly needed quantitative data on the Breakup of the Precorneal Tear Film. The effects of a number of variables in examining techniques and correlation of values obtained with age, sex and corneal sensitivity will be studied. These studies are directed to the development of a standard method for a clinical test of breakup-time. In addition, preliminary work by this investigator and associates has shown that breakup is accelerated in mucin-deficient dry eye states. Further necessary quantification of this data will be gathered to clearly define the limits for abnormal results. Finally, the use of the breakup-time of the precorneal tear film as a physiological test of the duration and efficacy of tear substitutes and ophthalmic vehicles will be studied.